This invention relates to mechanical face seals and, more particularly, to a simplified mechanical face seal arrangement that eases assembly and utilizes fewer parts than conventional shaft seal assemblies.
Conventional mechanical face seals are used in rotating equipment, such as gas turbine engines, to provide a fluid seal between regions of high and low fluid pressure. For example, mechanical face seals are used for sealing a rotating shaft on a pump, compressor, agitator, gas turbine, or other rotating equipment. In gas turbine engines, mechanical face seals are used to prevent hot, high pressure air from entering a bearing compartment that operates at a lower pressure and temperature.
A conventional metal-backed face seal arrangement for a gas turbine engine includes an annular graphitic carbon ring secured to a rotationally static, axially translatable, annular metal seal housing. A seal seat is affixed to a rotatable engine main shaft and positioned axially adjacent to the graphitic carbon ring. A nose of the annular graphitic carbon ring is urged into contact with the seal seat by a combination of spring forces acting on the seal housing and the net resultant of axially opposing fluid pressure forces. The contact between the nose and the seal seat resists fluid leakage across the seal arrangement in the radial direction.
Typically, a conventional graphitic carbon ring mechanical face seal arrangement includes between six and twelve spring guides affixed to a non-rotatable support or seal housing. The seal housing axially translates along the spring guides. A coil spring is arranged coaxially about each spring guide between the seal housing and the support to provide a bias force that urges the graphitic carbon ring into contact with the seal seat. Disadvantageously, the six to twelve spring guides and six to twelve corresponding coil springs are time consuming to install and add expense to the arrangement. Functionally, the seal seat limits movement of the seal arrangement in one axial direction, however, only the support limits movement in the opposite direction. This may undesirably damage the support and seal arrangement, or over-compress and over-stress one or more of the coil springs.
Accordingly, there is a need for a simplified and robust gas turbine engine shaft seal arrangement that is easy to install and has relatively few parts.